The invention relates to a direction sensitive counting and switching device comprising an optical system. The optical system includes a passive infrared detector that has sensor elements for detecting radiation transmitted along a beam path from persons or objects moving through a detection area of the detector and producing output signals in response to the detected radiation. A preamplifier coupled to the detector produces amplified output signals from the output signals from the sensor elements. A subsequently connected evaluation circuit initiates a counting and switching process from the output signals emitted by the sensor elements. The counting and switching process contains information about the direction of movement of a respective person or object.
Direction selective counting and switching devices are employed to count persons and/or objects that move or are moved in different directions. They furnish additional information about the direction of movement of the detected persons and/or objects.
According to the prior art, the counting and the determination of the direction of moving persons/objects has been realized in the past as follows:
When photoelectric barriers are employed, at least two beam transmitters and receivers are attached at each location to be monitored. A precise determination of moving objects/persons is possible only if they cross these barriers in succession.
For traffic monitoring, a loop technology is often employed. For this purpose, induction loops are installed in all traffic lanes. The high installation costs and the traffic impairment caused during the installation of the induction loops are disadvantageous.
Image processing devices are also suitable for a determination of the number and direction of moving objects. However, since these devices pick up signals from moving and non-moving objects, the costs for computer image processing are very high and the devices are therefore relatively expensive.
European Patent 0,287,827 discloses a direction selective pyrodetector which is composed of a sensor equipped with at least two sensor elements for different detection directions and is employed for the detection and velocity determination of moving objects. Since vehicles traveling next to one another are not resolved individually, an accurate count is not possible here.
Another solution, disclosed in European Patent 0,245,842 provides that a plurality of pyroelectric sensor elements are disposed within a mirror of spherical-parabolic shape and it thus becomes possible to perform a detection that is independent of motion and direction. The drawbacks are that objects moving next to one another are not detected individually, the complicated mirror is too expensive for many applications and the frequent requirement for small, unobtrusive detection systems is not met.
According to German Patent 3,407,462 it is possible to realize, for example, a door opener by means of two mutually at least partially covering infrared sensors which have a radiation sensitive surface corresponding to the shape of the desired field of view. Such a door opener does not record persons passing by the door; it responds only to persons directly approaching the door. Thus the door opener is direction selective in only one direction.
Further, German Unexamined Published Patent Application DE-OS 3,225,264 discloses an infrared motion sensor which switches on the illumination of hallways, lobbies, etc. for a predetermined time if persons move through the detection area of the motion sensor. The use of this solution, for example, as a light switch in homes is not possible since, although the illumination in a room is switched on when a person enters it, the light is switched off again at the end of the predetermined period of time if the person in the room does not continue to move.
German Patent 3,623,792 discloses a device employs a plurality of individual infrared sensors that are arranged behind one another in the direction of passage and next to one another transversely to the direction of passage to determine the number of persons and their direction of movement within a room to be monitored or in a passageway. Since the individual sensors have very large fields of view, this device cannot be employed in cases where only very narrow or small fields of view can be realized. Moreover, the use of individual sensors prevents this device from being miniaturized.
In public transportation systems, the number of passengers is analyzed primarily by photoelectric barriers, pressure sensors and sensitive floorboards.
In connection with the use of photoelectric barriers, two radiation transmitters and two radiation receivers are installed at each door of the public transportation means. The successive passage through both photoelectric barriers initiates a counting process which corresponds to the direction of movement of the passenger. Since, however, persons moving closely next to one another cannot be reliably detected individually and objects carried by passengers, such as umbrellas and handbags, are frequently counted as well, a precise determination of the number of passengers is not possible.
In buses, pressure sensors are known to be used at their shock absorbers. Since the number of passengers is determined from the weight of the bus, the determination of their number is not very precise. The pressure sensors cannot be employed in streetcars and railroad trains because of the high weight of the vehicles themselves.
German Unexamined Published Patent Application DE-OS 3,832,428 discloses a device of the above mentioned type. In this device, however, it is not exclusively the moving objects or persons but also non-moving targets within the detection area that are evaluated so that the results are imprecise.